Spear-guns of the general type indicated are well known. They typically employ rubbers which lie along the sides and top of the barrel and which are anchored at their forward ends to lugs on the top of the head of the barrel. The rear ends of the rubbers are joined together by a U-shape wire sling. To load such a spear-gun, a spear is first threaded rearward through a guide tube (formed in an upwards extension of the barrel head) so as to lie on top of the barrel, the butt end of the spear having a first notch for engagement with the trigger mechanism and a second notch--forward of the first--for engagement with the wire sling. Then, the spear is engaged with the trigger mechanism and the sling is drawn rearwards (against the tension of the rubbers) until it can be engaged with arid retained by the corresponding notch in the spear.
To fire, the gun is held by the pistol-grip, the barrel is pointed at a target and the trigger mechanism operated to release the spear which is then driven along the barrel and through the guide tube in the head by the sling and the rubbers, the spear, rubbers and guide tube being essentially in the same plane. To maximise the energy imparted to the spear, strong rubbers are used, but these require great strength to draw and, when they are at full-stretch, it is difficult for a user to properly and quickly engage the sling in its notch on the spear. Unless engagement is effected quickly, the arms of the person loading the gun will become exhausted and rubbers must be allowed to return to their relaxed position until re-loading can be attempted. As such a gun cannot be loaded in stages, the strength of the rubbers is normally chosen so that the gun can be readily loaded by an average person under water, thus greatly restricting it potential range.
The accuracy of the conventional spear gun--particularly one that uses strong rubbers--is badly affected by the asymmetrical forces on the barrel. Because the force of the rubbers acts approximately on the axis of the spear and not the barrel, the extended rubbers bend the ends of the barrel of a loaded gun upwards. When the gun is fired, the front end of the barrel will therefore whip downwards upon release of the rubber tension, throwing the spear off-course. Furthermore, because the spear is retained against the force of the rubbers by the engagement of a catch in the trigger mechanism with a small notch in the rear end of its narrow shaft, loaded guns of this type are prone to accidental discharge. Finally, it will be seen that conventional spear guns are inconvenient to load, particularly if they have long barrels, because of the need to thread the butt end of the spear through the guide tube in the head of the barrel.